There are various types of cartilage, e.g., hyaline cartilage and fibrocartilage. Hyaline cartilage is found at the articular surfaces of bones, e.g., in the joints, and is responsible for providing the smooth gliding motion characteristic of moveable joints. Articular cartilage is firmly attached to the underlying bones and measures typically less than 5 mm in thickness in human joints, with considerable variation depending on joint and site within the joint. In addition, articular cartilage is aneural, avascular, and alymphatic. In adult humans, this cartilage derives its nutrition by a double diffusion system through the synovial membrane and through the dense matrix of the cartilage to reach the chondrocyte, the cells that are found in the connective tissue of cartilage.
Adult cartilage has a limited ability of repair; thus, damage to cartilage produced by disease, such as rheumatoid and/or osteoarthritis, or trauma can lead to serious physical deformity and debilitation. Furthermore, as human articular cartilage ages, its tensile properties change. The superficial zone of the knee articular cartilage exhibits an increase in tensile strength up to the third decade of life, after which it decreases markedly with age as detectable damage to type II collagen occurs at the articular surface. The deep zone cartilage also exhibits a progressive decrease in tensile strength with increasing age, although collagen content does not appear to decrease. These observations indicate that there are changes in mechanical and, hence, structural organization of cartilage with aging that, if sufficiently developed, can predispose cartilage to traumatic damage.
For example, the superficial zone of the knee articular cartilage exhibits an increase in tensile strength up to the third decade of life, after which it decreases markedly with age as detectable damage to type II collagen occurs at the articular surface. The deep zone cartilage also exhibits a progressive decrease in tensile strength with increasing age, although collagen content does not appear to decrease. These observations indicate that there are changes in mechanical and, hence, structural organization of cartilage with aging that, if sufficiently developed, can predispose cartilage to traumatic damage.
Once damage occurs, joint repair can be addressed through a number of approaches. One approach includes the use of matrices, tissue scaffolds or other carriers implanted with cells (e.g., chondrocytes, chondrocyte progenitors, stromal cells, mesenchymal stem cells, etc.). These solutions have been described as a potential treatment for cartilage and meniscal repair or replacement. However, clinical outcomes with biologic replacement materials such as allograft and autograft systems and tissue scaffolds have been uncertain since most of these materials cannot achieve a morphologic arrangement or structure similar to or identical to that of normal, disease-free human tissue it is intended to replace. Moreover, the mechanical durability of these biologic replacement materials remains uncertain.
Usually, severe damage or loss of cartilage is treated by replacement of the joint with a prosthetic material, for example, silicone, e.g. for cosmetic repairs, or metal alloys. See, e.g., U.S. Pat. No. 6,383,228 to Schmotzer, issued May 7, 2002; U.S. Pat. No. 6,203,576 to Afriat et al., issued Mar. 20, 2001; U.S. Pat. No. 6,126,690 to Ateshian, et al., issued Oct. 3, 2000. Implantation of these prosthetic devices is usually associated with loss of underlying tissue and bone without recovery of the full function allowed by the original cartilage and, with some devices, serious long-term complications associated with the loss of significant amount of tissue and bone can include infection, osteolysis and also loosening of the implant.
Further, joint arthroplasties are highly invasive and often require surgical resection of the entirety or the majority of the articular surface of one or more bones. With these procedures, the marrow space is often reamed in order to fit the stem of the prosthesis. The reaming results in a loss of the patient's bone stock. U.S. Pat. No. 5,593,450 to Scott et al. issued Jan. 14, 1997 discloses an oval domed shaped patella prosthesis. The prosthesis has a femoral component that includes two condyles as articulating surfaces. The two condyles meet to form a second trochlear groove and ride on a tibial component that articulates with respect to the femoral component. A patella component is provided to engage the trochlear groove. U.S. Pat. No. 6,090,144 to Letot et al. issued Jul. 18, 2000 discloses a knee prosthesis that includes a tibial component and a meniscal component that is adapted to be engaged with the tibial component through an asymmetrical engagement.
Another joint subject to invasive joint procedures is the hip. U.S. Pat. No. 6,262,948 to Storer et al. issued Sep. 30, 2003 discloses a femoral hip prosthesis that replaces the natural femoral head. U.S. Patent Publications 2002/0143402 A1 and 2003/0120347 to Steinberg published Oct. 3, 2002 and Jun. 26, 2003, respectively, also disclose a hip prosthesis that replaces the femoral head and provides a member for communicating with the ball portion of the socket within the hip joint.
A variety of materials can be used in replacing a joint with a prosthetic, for example, silicone, e.g. for cosmetic repairs, or suitable metal alloys are appropriate. Implantation of these prosthetic devices is usually associated with loss of underlying tissue and bone and, with some devices, serious long-term complications associated with the loss of significant amounts of tissue and bone can cause loosening of the implant. One such complication is osteolysis. Once the prosthesis becomes loosened from the joint, regardless of the cause, the prosthesis will then often be required to be replaced. Since the patient's bone stock is limited, the number of possible replacement surgeries is also limited for joint arthroplasty.
As can be appreciated, joint arthroplasties are generally highly invasive procedures and can require surgical resection of the entirety, or a majority of, the articular surface of one or more bones involved in the repair. In many procedures, the marrow space can be fairly extensively reamed in order to fit the stem of the prosthesis within the bone. Reaming results in a loss of the patient's bone stock and over time subsequent osteolysis will frequently lead to loosening of the prosthesis. Further, the area where the implant and the bone mate degrades over time requiring the prosthesis to eventually be replaced. Since the patient's bone stock is limited, the number of possible replacement surgeries can be limited for joint arthroplasty. In short, over the course of 15 to 20 years, and in some cases even shorter time periods, the patient can run out of therapeutic options ultimately resulting in a painful, non-functional joint.
In the past, a diseased, injured or defective joint, such as, for example, a joint exhibiting osteoarthritis, was repaired using standard off-the-shelf implants and other surgical devices. Specific off-the-shelf implant designs have been altered over the years to address particular issues. For example, several existing designs include implant components having rotating parts to enhance joint motion. Ries et al. describes design changes to the distal or posterior condyles of a femoral implant component to enhance axial rotation of the implant component during flexion. See U.S. Pat. Nos. 5,549,688 and 5,824,105. Andriacchi et al. describes a design change to the heights of the posterior condyles to enhance high flexion motion. See also U.S. Pat. No. 6,770,099. However, in altering a design to address a particular issue, historical design changes frequently have created one or more additional issues for future designs to address. Collectively, many of these issues have arisen from one or more differences between a patient's existing joint anatomy and the corresponding features of an implant component.
Joint implants have historically employed a one-size-fits-all (or a few-sizes-fit-all) approach to implant design. A series of one or more “standard” implant shapes and/or sizes is pre-manufactured and stockpiled, and then one or more of these implants selected for implantation in the patient. It has been common practice to modify the patient's anatomical support structures (e.g., cut supporting bones and/or other structures) to accommodate a chosen implant, and with a limited number of shapes and sizes to of implants choose from, it is virtually guaranteed that the chosen implant will not be a “perfect fit” to the patient's anatomy. Rather, the chosen implant is likely the “best fit” or best compromise available, with the surgical procedure still requiring removal of significant bone and/or other support tissues to accommodate the chosen implant size. Accordingly, advanced implant designs and related devices and methods that address the needs of individual patient's are needed.
Moreover, currently available devices do not optimally provide ideal alignment with the articular surfaces and the resultant joint congruity. Poor alignment and poor joint congruity can, for example, lead to instability of the joint. In the knee joint, instability typically manifests as a lateral instability of the joint.
Thus, there remains a need for compositions for joint repair, including methods and compositions that facilitate the integration between the cartilage replacement system and the surrounding cartilage. There is also a need for tools that increase the accuracy of cuts made to the bone in a joint in preparation for surgical implantation of, for example, an artificial joint.